This invention pertains to the measurement of displacements, particularly displacements wherein the reference point, the point being displaced, is not fixed. Collective control systems in helicopters are representative of such reference points. In one of its aspects this invention relates to maintaining control systems of helicopters. In another aspect, the invention provides an adjusting tool for use in rigging helicopter control systems.
The usual control of a helicopter during its operation is achieved by varing the pitch of its rotor blades. When the pitch angle of a particular rotor blade is changed as the rotor rotates, this change introduces cyclic pitch. Hence, the mechanical system which changes pitch angles of particular blades is the cyclic control system. If, on the other hand, the mechanical system changes the pitch angles of each of the rotor blades the same amount, collective pitch is introduced. Collective pitch is accomplished by the collective control system.
Cyclic and collective control are achieved in some helicopters by raising and lowering the swashplate. In other helicopter models, a sissors and sleeve assembly is employed. In either event, the swashplate or the sleeve must be raised, or lowered, within very precise and narrow limits in order to maintain the blade angles of attack within design limitations, and to coordinate those pitch angles with flight parameters, particularly negative collective control in the case of autorotation. To this end precise rigging of the collective control system is necessary. This invention provides a gauge which makes this rigging easier to effect.